1. Field of the Invention
The present invention relates to well cementing methods and compositions.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in the construction and repair of oil and gas wells. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casing or liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented. Hydraulic cement compositions are also commonly used to plug lost circulation and other undesirable fluid inflow and outflow zones in wells, to plug cracks or holes in pipe strings cemented therein and to accomplish other required remedial well operations.
In order for such well cementing operations to be successful, the cement compositions utilized must include a fluid loss control additive to reduce the loss of fluid, i.e., water, from the cement compositions when they contact permeable subterranean formations or zones. Excessive fluid loss causes a cement composition to be prematurely dehydrated which limits the amount of cement composition that can be pumped, decreases the compressive strength of the cement composition and prevents or reduces bond strength between the set cement composition and a subterranean zone, the walls of pipe and/or the walls of the well bore.
Heretofore polymers and copolymers have been utilized as fluid loss control additives for well cements. A particularly suitable copolymer which has been utilized as a cement composition fluid loss control additive is a copolymer of 2-acrylamido-2-methyl propane sulfonic acid and N,N-dimethylacrylamide having mole ratios of 2-acrylamido-2-methyl propane sulfonic acid to N,N-dimethylacrylamide of between 1:4 and 4:1 respectively, and having an average molecular weight of between about 75,000 and 3,000,000. While the above described copolymer well cement fluid loss control additive has achieved commercial success, there is a continuing need for improved polymer fluid loss control additives which achieve better fluid loss control in well cement compositions.
The present invention provides well cementing methods and compositions which include improved liquid fluid loss control additives comprised of water soluble polymers which meet the need described above and overcome the deficiencies of the prior art. The water soluble fluid loss control polymer additives which are useful in accordance with this invention are comprised of the following monomers:
a) 5 to 93 weight % of monomers of the formula (Ia) or (Ib) or both 
xe2x80x83wherein
R1 is hydrogen or C1-C5 alkyl,
R2 is C1-C20 alkylene, carboxy C1-C20 alkylene, carboamido C1-C20 alkylene or phenylene,
M is hydrogen, ammonium or a metal cation in the oxidation state +I, +II or +III and
x is 1 to 3;
b) 1 to 50 weight % of monomers of the formula (IIa) or (IIb) or both 
xe2x80x83wherein
R3 and R4 are xe2x80x94COOxe2x88x92(Mx+)1/x or 
R5 is xe2x80x94COOxe2x88x92(Mx+)1/x,
M is hydrogen, ammonium or a metal cation in the oxidation state +I, +II or +III and
x is 1 to 3;
c) 5 to 93 weight % of a monomer of the formula (III) 
xe2x80x83wherein
R6 is hydrogen or C1-C5 alkyl,
R7 and R8 are hydrogen, C1-C10 alkyl or xe2x80x94(CH2)yxe2x80x94 and
y is 3 to 7; and
d) 1 to 25 weight % of monomers of the formula (IVa) or (IVb) or both 
xe2x80x83wherein
R9 is hydrogen or C1-C5 alkyl,
R10 is C1-C10 alkyl, C1-C10 aminoalkyl, C1-C20 hydroxyalkyl, C1-C4 alkyl or hydroxyl terminated mono- or poly-C2-C3 alkylenoxy (with 1 to 400 alkylenoxy units), C7-C20 alkylaryl, C7-C20 hydroxyalkylaryl, C6-C10 aryl or C6-C10 hydroxyaryl,
R11, R12 and R13 are hydrogen or C1-C5 alkyl and
R14 is hydrogen, C1-C20 alkyl, C1-C10 aminoalkyl, C1-C20 hydroxyalkyl, C1-C4 alkyl- or hydroxyl terminated mono- or poly-C2-C3 alkylenoxy (with 1 to 400 alkylenoxy units), C7-C20 alkylaryl, C7-C20 hydroxyalkylaryl, C6-C10 aryl, C6-C10 hydroxyaryl or with hydroxyl substituted C1-C20 alkylensulfonic acids and their ammonium, alkali metal or alkaline earth metal salts; and
wherein the monomers a) to d) add up to 100 weight %.
The methods of this invention for cementing a subterranean zone penetrated by a well bore are basically comprised of the following steps. A cement composition is provided comprised of a hydraulic cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive as described above. The composition is placed into the subterranean zone to be cemented and then allowed to set into an impermeable solid mass therein.
The cement compositions of this invention are basically comprised of a hydraulic cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive as described above.
A preferred fluid loss control polymer additive useful in this invention is a polymer containing the calcium salt of 2-acrylamido-2-methyl propane sulfonic acid in an amount of about 69 weight %, the calcium salt of maleic acid in an amount of about 14 weight %, N-vinyl caprolactam in an amount of about 14 weight % and 4-hydroxybutyl vinyl ether in an amount of about 3 weight %. The polymer additive has a molecular weight of about 250,000.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
The methods of the present invention for cementing a subterranean zone penetrated by a well bore are basically comprised of the following steps. A cement composition is provided comprised of a hydraulic cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive. The cement composition is placed in the zone to be cemented and thereafter the cement composition is allowed to set into an impermeable solid mass therein. The placement of the cement composition is usually accomplished by pumping the cement composition through the well bore and into the zone to be cemented.
The cement compositions of this invention are basically comprised of hydraulic cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive.
A variety of hydraulic cements can be utilized in accordance with the present invention including, but not limited to, Portland cements, pozzolana cements, gypsum cements, aluminous cements and silica cements. Portland cements are generally preferred with the types defined and described in API Specification For Materials And Testing For Well Cements, API Specification 10, 5th Edition, dated Jul. 1, 1990 of the American Petroleum Institute being particularly suitable. Preferred such API Portland cements include classes A, B, C, G and H with API classes G and H being more preferred.
The water in the cement compositions can be fresh water or salt water. The term xe2x80x9csalt waterxe2x80x9d includes unsaturated salt solutions and saturated salt solutions including brines and seawater. Generally, any water can be utilized so long as it does not adversely affect components of the well cement composition. The water is generally present in a cement composition of this invention in an amount sufficient to form a pumpable slurry, i.e., in an amount in the range of from about 30% to about 120% by weight of cement in the composition. The water is generally present in the cement composition in an amount in the range of from about 35% to about 100% by weight of hydraulic cement therein.
As mentioned above, the polymeric fluid loss control additives useful in accordance with this invention are water soluble polymers containing four different monomers, the principal monomer being an olefinic sulfonic acid.
More specifically, the fluid loss control polymers contain:
a) 5 to 93 weight % of monomers of the formula (Ia) or (Ib) or both 
xe2x80x83wherein
R1 is hydrogen or C1-C5 alkyl,
R2 is C1-C20 alkylene, carboxy C1-C20 alkylene, carboamido C1-C20 alkylene or phenylene,
M is hydrogen, ammonium or a metal cation in the oxidation state +I, +II or +III and
x is 1 to 3;
b) 1 to 50 weight % of monomers of the formula (IIa) or (IIb) or both 
xe2x80x83wherein
R3 and R4 are xe2x80x94COOxe2x88x92(Mx30 )1/x or 
R5 is xe2x80x94COOxe2x88x92(Mx30 )1/x,
M is hydrogen, ammonium or a metal cation in the oxidation state +I, +II or +III and
x is 1 to 3;
c) 5 to 93 weight % of a monomer of the formula (III) 
xe2x80x83wherein
R6 is hydrogen or C1-C5 alkyl,
R7 and R8 are hydrogen, C1-C10alkyl or xe2x80x94(CH2)yxe2x80x94 and
y is 3 to 7;
and
d) 1 to 25 weight % of monomers of the formula (IVa) or (IVb) or both 
xe2x80x83wherein
R9 is hydrogen or C1-C5 alkyl,
R10 is C1-C10 alkyl, C1-C10 aminoalkyl, C1-C20 hydroxyalkyl, C1-C4 alkyl or hydroxyl terminated mono- or poly-C2-C3 alkylenoxy (with 1 to 400 alkylenoxy units), C7-C20 alkylaryl, C7-C20 hydroxyalkylaryl, C6-C10 aryl or C6-C10 hydroxyaryl,
R11, R12 and R13 are hydrogen or C1-C5 alkyl and
R14 is hydrogen, C1-C20 alkyl, C1-C10 aminoalkyl, C1-C20 hydroxyalkyl, C1-C4 alkyl- or hydroxyl terminated mono- or poly-C2-C3 alkylenoxy (with 1 to 400 alkylenoxy units), C7-C20 alkylaryl, C7-C20 hydroxyalkylaryl, C6-C10 aryl, C6-C10 hydroxyaryl or with hydroxyl substituted C1-C20 alkylensulfonic acids and their ammonium, alkali metal or alkaline earth metal salts; and
wherein the monomers a) to d) add up to 100 weight %.
R1 and R2 of the monomers of the formulas (Ia) and (Ib) of the fluid loss control polymers of this invention are preferably hydrogen and xe2x80x94COxe2x80x94NHxe2x80x94C(CH3)2xe2x80x94CHxe2x80x94, respectively, and M in the monomers of the formulas (Ia), (Ib), (IIa) and (IIb) are preferably metal cations wherein the +I metal cations are alkali metal ions, most preferably sodium or potassium ions, the +II metal cations are alkaline earth metal ions, most preferably calcium or magnesium ions and the +III metal cations are aluminum or iron ions.
In the monomer of the formula (III) y is preferably 3 to 5, and in the monomers of the formulas (IVa) and (IVb) when R10 and R14 are C1-C20 hydroxyalkyl, C7-C20 hydroxyalkylaryl or C6-C10 hydroxyaryl moieties, the moieties can contain one or more hydroxyl functionalities.
In the monomers of the formulas (IVa) and (IVb), R9 is preferably hydrogen and R10 is preferably one of C1-C6 hydroxylalkyl, methyl or hydroxyl terminated mono or poly C2-C3 alkenoxy residue. In the monomer of the formula (IVb), R11, R12 and R13 are preferably hydrogen and R14 is preferably 2,3-dihydroxypropyl sulfonic acid, 3-hydroxypropyl sulfonic acid or 2-hydroxypropyl-3-sulfonic acid or the ammonium, alkali metal or alkaline earth metal salts thereof.
The fluid loss control polymers preferably contain 40 to 83 weight % of the monomers of the formulas (Ia), (Ib) or both, 5 to 48 weight % of the monomers of the formulas (IIa), (IIb) or both, 10 to 53 weight % of the monomer of the formula (III) and 1 to 10 weight % of the monomers of the formulas (IVa), (IVb) or both.
The fluid loss control polymers preferably have molecular weights in the range of from 10,000 to 3,000,000 grams per mole, more preferably in the range of from 100,000 to 1,000,000 grams per mole.
A particularly preferred fluid loss control polymer of this invention is comprised of 69 weight % of the calcium salt of 2-acrylamido-2-methyl propane sulfonic acid (I), 14 weight % of the calcium salt of maleic acid (II), 14 weight % of N-vinyl caprolactam (III) and 3 weight % of 4-hydroxybutyl vinyl ether (IV).
The fluid loss control polymer additives of this invention can be prepared using known polymerization techniques.
A fluid loss control polymer additive as described above is included in a cement composition of this invention in an amount in the range of from about 0.1% to about 2% by weight of cement in the composition.
As will be understood by those skilled in the art, a variety of other well cement composition additives known to those skilled in the art can be included in the cement compositions of this invention. Such additives include, but are not limited to, set retarding additives, set accelerating additives, dispersing agents, lightweight additives and the like.
A preferred method of cementing a subterranean zone penetrated by a well bore of this invention is comprised of the steps of: (a) providing a cement composition comprising a hydraulic cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive comprised of 69 weight % of the calcium salt of 2-acrylamido-2-methyl propane sulfonic acid, 14 weight % of the calcium salt of maleic acid, 14 weight % of N-vinyl caprolactam and 3 weight % of 4-hydroxybutyl vinyl ether; (b) placing the composition in the zone to be cemented; and (c) allowing the cement composition to set into an impermeable solid mass therein.
A more preferred method of cementing a subterranean zone penetrated by a well bore is comprised of the steps of: (a) providing a cement composition comprising Portland cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive comprised of 69 weight % of the calcium salt of 2-acrylamido-2-methyl propane sulfonic acid, 14 weight % of the calcium salt of maleic acid, 14 weight % of N-vinyl caprolactam and 3 weight % of 4-hydroxybutyl vinyl ether present in the cement composition in an amount in the range of from about 0.1% to about 2% by weight of hydraulic cement therein; (b) placing the composition in the zone to be cemented; and (c) allowing the cement composition to set into an impermeable solid mass therein.
A preferred well cement composition of this invention comprises a hydraulic cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive comprised of 69 weight % of the calcium salt of 2-acrylamido-2-methyl propane sulfonic acid, 14 weight % of the calcium salt of maleic acid, 14 weight % of N-vinyl caprolactam and 3 weight % of 4-hydroxybutyl vinyl ether.
A more preferred well cement composition comprises Portland cement, sufficient water to form a pumpable slurry and a fluid loss control polymer additive comprised of 69 weight % of the calcium salt of 2-acrylamido-2-methyl propane sulfonic acid, 14 weight % of the calcium salt of maleic acid, 14 weight % of N-vinyl caprolactam and 3 weight % of 4-hydroxybutyl vinyl ether present in the well cement composition in an amount in the range of from about 0.1% to about 2% by weight of cement in the composition.
In order to further illustrate the well cementing methods, compositions and additives of the present invention, the following example is given.